Study sheet: Pressure Winds Storms and Cyclones

📋 Course Outline

1. Pressure and Force Area Relations
2. Pressure in Liquids
3. Atmospheric Pressure
4. Air Pressure and Wind Formation
5. High-Speed Winds and Roofs
6. Storms and Thunderstorms
7. Lightning and Electrical Safety
8. Cyclone Formation and Structure
9. Cyclone Hazards and Protection

📖 1. Pressure and Force Area Relations

🔑 Key Concepts & Definitions

• Pressure : The force acting per unit area, considering forces perpendicular to the surface.

★ Must-know

📐 Formula — Pressure satisfies $P = \frac{F}{A}$, where F is force and A is area.

• A force of 100 N acting on an area of 2 m² produces a pressure of 50 N/m².

📌 Increasing the area over which a force acts reduces pressure, so broad bag straps, broad bucket handles, and cloth rings under loads make carrying more comfortable.

Further detail

• The SI unit of pressure is the newton per square metre, written N/m², which is also called the pascal and denoted Pa.

💡 Memory Hook

Broad straps spread force; narrow straps concentrate force.

📖 2. Pressure in Liquids

🔑 Key Concepts & Definitions

• Liquid pressure : The pressure exerted by a liquid on the surfaces surrounding it.

★ Must-know

• A pointed nail and the sharp edge of a knife exert greater pressure because their smaller contact areas concentrate the applied force.

📌 The pressure exerted by a liquid increases as the height of its liquid column increases.

• Overhead water tanks are placed at a height so that the increased liquid pressure produces a stronger stream of water from taps.

Further detail

• Equal heights of water columns produce equal bulges in balloons attached to pipes of different diameters.

• The base of a dam is broader than its top because horizontal water pressure is very large near the bottom and the broad base withstands it.

💡 Memory Hook

Greater liquid-column height → greater pressure at the bottom.

📖 3. Atmospheric Pressure

🔑 Key Concepts & Definitions

• Atmospheric pressure : The pressure exerted by the air surrounding us.

★ Must-know

• A rubber sucker sticks to a smooth surface because pressing it out reduces the air pressure inside, while the surrounding atmospheric pressure remains higher.

Further detail

• The atmosphere contains nitrogen, oxygen, argon, carbon dioxide, and other gases in small quantities and extends many kilometres above Earth’s surface.

• The atmospheric force on an area of 15 cm × 15 cm is nearly equal to the gravitational force on a 225 kg mass, or about 2250 N.

• The practical unit of air pressure is the millibar, and one millibar or one hectopascal equals 100 Pa.

💡 Memory Hook

A giant invisible air column presses on every surface.

📖 4. Air Pressure and Wind Formation

★ Must-know

📌 Air moves from a region of higher air pressure to a region of lower air pressure until the pressures become equal.

• During the day, land heats faster than water, warm air above the land rises and creates low pressure, and cooler air from the sea moves toward the land as a sea breeze.

Further detail

• At night, water remains warmer than land, low pressure develops above the sea, and air moves from the land to the sea as a land breeze.

• A greater difference in air pressure produces faster air movement.

💡 Memory Hook

High pressure → low pressure → air movement.

📖 5. High-Speed Winds and Roofs

★ Must-know

• Blowing between two balloons creates a low-pressure region between them, so the higher surrounding pressure pushes the balloons together.

📌 High-speed winds are accompanied by reduced air pressure.

📌 During a storm, opening doors and windows can reduce the pressure difference between the air inside a house and the air above its roof, helping prevent the roof from being blown away.

Further detail

• A roof with weak construction may be blown away when high-speed winds create much lower pressure above it than below it.

💡 Memory Hook

Faster wind → lower pressure above roofs → possible roof damage.

📖 6. Storms and Thunderstorms

🔑 Key Concepts & Definitions

• Storm : Strong wind accompanied by rain.
• Thunderstorm : A storm accompanied by lightning and thunder.

★ Must-know

• Storm formation involves warm moist air rising, cooling and condensing into clouds, cloud droplets merging into heavier drops, and precipitation falling as rain, hail, or snow.

Further detail

• Storms are more frequent in hot, humid, and tropical regions such as India.

💡 Memory Hook

Warm moist air rises → clouds form → rain falls → storms develop.

📖 7. Lightning and Electrical Safety

🔑 Key Concepts & Definitions

• Lightning : A sudden flow of electric charges that produces a bright flash when the insulating property of air breaks down.
• Lightning conductor : A pointed metal rod with one end higher than a building and the other end buried deep in the ground, providing an easy path for electric charges.

★ Must-know

• Strong upward and downward winds make water droplets and ice particles rub together, causing positive and negative electric charges to develop and separate within clouds.

Further detail

• Lightning can occur within a cloud, between clouds, or between a cloud and the ground.

📌 During lightning, people should avoid tall objects and water, crouch in a low-lying open area without lying flat, avoid metal-rod umbrellas, and remain comparatively safer inside a bus or car.

💡 Memory Hook

Charge separation → air breakdown → lightning → thunder.

📖 8. Cyclone Formation and Structure

🔑 Key Concepts & Definitions

• Cyclone : A spinning system of clouds, winds, and rain formed around a very low-pressure area, with high-speed winds revolving around it.
• Eye of the cyclone : The central region of lowest pressure where the wind is calm, while the surrounding region has strong winds and heavy rainfall.

★ Must-know

• A cyclone forms when warm ocean water heats moist air, the air rises and condenses, released heat makes it rise further and lowers pressure, surrounding air rushes in, and Earth’s rotation makes the moving air spin.

Further detail

📌 A cyclone gradually loses strength after reaching land because its source of moist air is cut off.

💡 Memory Hook

Warm ocean → rising moist air → low pressure → spinning winds.

📖 9. Cyclone Hazards and Protection

★ Must-know

• Cyclone-driven ocean-water surges can form a wall of water 3–12 metres high and flood coastal areas and regions farther from the sea.

• Cyclone impacts include:

  • Heavy rainfall
  • River overflow
  • Landslides
  • Contaminated drinking water
  • Less fertile soil
  • Blocked roads
  • Prolonged power outages

📌 Cyclone-prone communities should follow India Meteorological Department alerts, use satellite-based warnings, keep an emergency kit ready, and move to designated cyclone shelters.

Further detail

• The Amphan cyclone in 2020 had peak wind speeds of 270 km/h.

💡 Memory Hook

The cyclone eye is calm, whereas its surrounding wall has strong winds and rain.